Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/23/17

Area Forecast Discussion
National Weather Service Gaylord MI
855 PM EST Fri Dec 22 2017 .UPDATE... Issued at 854 PM EST Fri Dec 22 2017 Passing mid-level wave and attendant surface trough/weak low pressure continues to generate a large area of mostly light snow for areas along and north of M-32 this evening. Reductions in visibility have not been terribly impressive, on the order of 2 to 3 miles, indicating snowfall rates largely under a half inch per hour. Main area of snow expected to pivot off to the northeast in the next few hours as mid level support and deepest moisture axis do the same. Surface trough rotating west to east will likely drive a few more snow showers into the early morning hours, as will the development of a weak lake response. Not a big deal for sure, with additional snowfall amounts likely remaining under an inch for most. Aggressive drying noted just on the other side of Lake Michigan, and would not be surprised to see a few breaks in the overcast by later tonight across our neck of the woods. && .NEAR TERM...(Tonight through Saturday) Issued at 345 PM EST Fri Dec 22 2017 ...Burst of light/moderate snow north of M-68 thru this evening... High impact weather potential...snow early north of M-68. A wsw-ene oriented frontal zone was just south of MI this afternoon. An inverted trof extended north from western OH into nw lower MI and central upper MI. Snow has been intensifying (as expected) over far northern lower and central/eastern upper MI. After this system departs, nw flow lake effect will develop, and be most vigorous on Superior. Excellent agreement among the near-term models that light to moderate snow will fall over eastern upper and far northern lower MI over the next 6-8 hours. The HRRR now has QPF totals pushing 0.25" toward the mouth of the St Marys River, though this is very much on the high side of guidance. Still will kick up afternoon/evening snowfall totals to around 3" over a small portion of se Chippewa Co. Generally 1-2" across other areas north of M-68, with just patchy light snow and just maybe some drizzle/fzdz to the south. After that, deeper moisture departs, but colder air moves in. By 18Z Saturday, 850mb temps in the mid minus teens will be crossing Lakes MI and Superior. Given that we are somewhat moisture-deprived and inversion-limited (4-5k ft), we will see more lake convection on Superior, where the fetch is much longer. Snow showers are likely in nw Chippewa Co by late tonight, and especially on Saturday (when likely pops extend all the way to the Sault). Still, moisture and inversion issues will limit how vigorous this activity can be. Will keep accums on Saturday in central/western Chip Co in the 1-3" range. In the nw lower MI snowbelts, only chancy pops are in order. Anticipate a touch of sunshine away from the snowbelts in ne lower MI Saturday, especially in the morning. Min temps tonight upper teens to mid 20s. Max temps Saturday mid 20s to lower 30s. && .SHORT TERM...(Saturday night through Monday) Issued at 345 PM EST Fri Dec 22 2017 ...Turning sharply colder for Christmas with increasing lake effect activity... High Impact Weather Potential...Accumulating lake effect snow developing Sunday night into Christmas Day. Pattern Synopsis/Forecast...Broad longwave troughing will be found across the central CONUS as a deep cutoff low wobbles around Hudson Bay. A weak surface low will slide across southern Ontario late Saturday, stalling over eastern Lake Superior on Sunday where it will intensify somewhat as the upper trough sharpens overhead. Meanwhile a potent lobe of vorticity rounding the base of this trough will combine with warm air advection to produce a swath of snowfall across mainly the southern Great Lakes region on Sunday, which could brush southern portion of the APX forecast area. The aforementioned low over Lake Superior will slowly pull away from the region on Christmas Day, dragging a strong trailing cold front through northern Michigan. This will usher in a blast of Arctic air, leading to renewed lake effect snow chances. Primary Forecast Concerns...Falling temperatures and increasing snow chances heading into Sunday and Christmas Day. Weak warm air advection occurring Saturday night into Sunday morning across northern Michigan will warm 850mb temperatures ever so slightly. This will occur as somewhat drier air infiltrates northern Michigan thanks to a high pressure ridge, which will help keep lake effect snow chances largely in check for most areas (aside from northern Chippewa County). Heading into Sunday, the greatest concern will be snowfall potential from the system progged to trek across the Ohio Valley. Most models had been keeping the bulk of associated snowfall potential just south of the APX forecast area, but the 22.12Z ECMWF run has shifted the snow potential farther north. This would give all of northern Lower a chance of more widespread, synoptic type snow. Have nudged PoPs up a bit to account for this, but will have to watch how upcoming model runs trend. Temperatures aloft start to tumble Christmas Eve and really plummet through the day on Christmas (below -20C by Monday evening), which will prime the pump on the lake effect machine. Most ingredients will be very favorable initially for WNW flow snowbelts across northwest Lower with plenty of low level moisture, inversion heights to around 10 kft or a little higher, as well as strong low level omega and lapse rates. Wind fields will be a little trickier across eastern Upper with the surface trough in the vicinity, but generally WNW to NW flow up there. One limiting factor to snowfall accumulations over time will be the colder temperatures` impact on snow growth. Near surface temperatures will steadily drop through the day on Monday, which will lead to the DGZ becoming shallower with time and rooted nearly at the surface. Thus, snowflake growth will become less efficient with time, making it harder for snow to pile up as easily. Winds gusting to 20-30 mph during the day will lead to some blowing snow. Temperatures will climb into the mid 20s to lower 30s on Saturday, dropping into the teens across most of the area Saturday night. Sunday`s highs will be in the low to mid 20s with lows dropping back into the teens to single digits by Christmas morning. Very little recovery on Christmas with temperatures largely falling through the day. .LONG TERM...(Monday night through Friday) Issued at 345 PM EST Fri Dec 22 2017 High impact weather potential...Prolonged period of accumulating lake effect snow likely. Progressively colder 850mb temperatures will continue to pour into the region heading into Tuesday, with a /slow/ modification expected heading into the latter half of the week. This will lead to frigid conditions, especially each night, as lows drop into the single digits above/below zero. Factor in the winds, and wind chills will drop to around -10 to -20 degrees at times, mainly during the overnight hours. The other story will be a prolonged period of lake effect snow, generally in the WNW to NW flow snowbelts through Wednesday. Looking like Lake Huron will also come into play by Thursday and Friday as the wind pattern shifts around a bit. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 626 PM EST Fri Dec 22 2017 Light to moderate snow and IFR conditions expected for a few more hours yet at KPLN. Mostly MVFR cigs elsewhere with just some passing flurries. Expect slow improvement overnight as cigs lift some and snow exits. May see a bit of lake effect snow showers develop later tonight into Saturday, but this activity should largely fall between taf locations. Otherwise, expect a scattered/broken strato-cu field producing more MVFR/low end VFR conditions. Light winds through this taf period. && .MARINE... Issued at 345 PM EST Fri Dec 22 2017 Some gusty east winds will continue to diminish heading thru this evening. That will be replaced by nw winds late tonight and especially Saturday. Winds/waves will reach small craft advisory levels on many northern MI waters Saturday into Sat evening, before diminishing. && .APX WATCHES/WARNINGS/ADVISORIES... MI...NONE. LH...SMALL CRAFT ADVISORY until 11 PM EST this evening for LHZ347-348. LM...NONE. LS...SMALL CRAFT ADVISORY from 1 AM Saturday to 5 AM EST Sunday for LSZ321. && $$ UPDATE...MB NEAR TERM...JZ SHORT TERM...MK LONG TERM...MK AVIATION...MB MARINE...JZ
Area Forecast Discussion
National Weather Service Denver/Boulder CO
810 PM MST Fri Dec 22 2017 .UPDATE... Issued at 800 PM MST Fri Dec 22 2017 Have adjusted some of the near term winds to follow observations. Both HRRR and RAP have been hinting at fog over the far northeastern plains early Saturday morning as surface winds become southeasterly. However, considering the cloud cover that will be increasing, and looking at forecast soundings, not seeing how that could occur. Will leave out of the forecast for now. No adjustments needed to the winter storm timing or amounts, will keep the forecast ongoing. && .SHORT TERM...(This evening through Saturday) Issued at 217 PM MST Fri Dec 22 2017 Northwest flow aloft will increase tonight bringing Pacific moisture with it. Orographic lift will start to produce snow over the northern mountains around midnight. Snow is expected to become widespread over the mountains north of I-70 by 12Z Saturday. Lapse rates of 6-8 C/km below 500mb will help keep snow going through Saturday. Lift from the jet will produce bands of heavier snow over the mountains Saturday afternoon. Best lift, thus best snowfall is expect to fall over the north central mountains. The Winter Storm Warnings and Advisories still look on track with the heaviest snow falling over the mountains of Jackson and Grand counties. Snowfall amounts of 8 to 14 inches are expected over the northern mountains with 4 to 8 inches in the mountains along I-70. Locally higher amounts are expected due to the orographic nature of snow and banded snowfall. For the Front Range and eastern plains, temperatures will be cool tonight, but not as cold as last night. Skies will become mostly cloudy overnight and slow/stop cooling after midnight. Lows are expected to be in the teens with single digits likely in the cold low lying areas. Mostly cloudy skies will continue into Saturday and limit heating. This should result in cooler temperatures with highs mainly in the 30s. A cold front will enter northern Colorado around mid afternoon. Lift associated with the front and from the jet is expected to produce snow along the Wyoming/Colorado border late in the afternoon. This snow should drop south Saturday evening. .LONG TERM...(Saturday night through Friday) Issued at 217 PM MST Fri Dec 22 2017 A strong to moderate northwesterly flow aloft will be over the region through the middle of next week. Saturday night, a strong northwesterly flow aloft will be over with a 130 jet max over northwest CO at 00z translating eastward across CO through 12z Sunday. Northeast CO on the north side of the jet max and it a favorable location for Convective Symmetric Instability or CSI bands, from 00z-06z in the evening. Low level upslope developing behind the cold front through the evening, impacting areas around Fort Collins in the 00-03z period and Denver 03-06z time frame. Best chance of accumulating snowfall across the northeast plains will be over the northern tier zones with 1 to 2 inches possible, but will mention accumulations of an inch or less as far south as Denver. Locally higher amounts would be possible under enhanced banding. In the mountains, current timing of the highlights looks fine for now, with the snowfall decreasing by mid evening. The strong northwesterly flow aloft will continue through Monday. Mid level subsidence will allow for drier but continued cold conditions through most of Sunday. Another system associated with the next jet max is progged to drop out the northwest and bring additional snowfall primarily to the mountains Sunday night into Christmas Day. At this time, amounts in the 4-8 inch range not out of the question. A cold front push into the northeast plains Monday afternoon with a slight chance of snow especially north and east of Denver Monday afternoon into Monday night. A period of brief subsidence will occur Tuesday into Wednesday with a drier northwesterly flow aloft will be over the region. The flow aloft will be weakening at that time as well. The next system is expected to drop out of the northwest and into the northern mountains Wednesday night into Thursday, with a slight chance across the northeast plains Thursday morning. The flow aloft will increase at that time as well with the passage of the trough. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 800 PM MST Fri Dec 22 2017 High clouds will increase tonight with VFR conditions expected to prevail through 20-24Z Saturday. Southerly drainage winds, with gusty west winds likely later tonight at BJC, will extend tonight through most of the morning. At this point, the forecasted direction gets difficult as a surface low heads south into southeastern Colorado, but a trough that extends up along the urban corridor will either produce northeasterly winds at DEN and APA, or, gusty WNW prefrontal winds will push out from the foothills. For now will put DEN at N, and APA at NW being closer to the higher terrain. A cold front is expected over the airports around 02-04z, with lower ceilings and possible light banded snow expected soon after. && .BOU WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 2 AM to 11 PM MST Saturday for COZ034. Winter Storm Warning from 2 AM to 11 PM MST Saturday for COZ031- 033. && $$ UPDATE...Kriederman SHORT TERM...Meier LONG TERM...Cooper AVIATION...Meier
Area Forecast Discussion
National Weather Service Charleston SC
930 PM EST Fri Dec 22 2017 .SYNOPSIS... High pressure will prevail through Saturday, then a cold front will move through Sunday morning. High pressure will then rebuild through Tuesday. A series of upper disturbances could affect the area mid to late next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... NARRE-TL dense fog probabilities continue climb across Southeast Georgia with each hourly run. Already seeing vsbys as low as 1-3 miles south of the Altamaha River along with widespread stratus. Suspect a Dense Fog Advisory will likely be needed for parts of the area later tonight. Made minor adjustments to hourly temperatures per going trends noted at 23/02z, but the rest of the forecast is on track. The main concern overnight centers on the development of fog and stratus. The best fog parameters look align across Southeast Georgia after midnight where the lowest 1000 hPa condensation pressure deficits will be found. Light south to southwest winds will likely advect some of the fog and stratus north into southern South Carolina closer to daybreak. Given the persistent dense fog parameters noted in the NARRE-TL, H3R and RAP over the past few hours, will introduce dense fog wording for much of interior Southeast Georgia and expand the mention of patchy fog north into parts of the Charleston Tri-County area. Right now, dense fog is not expected in the Charleston Metro Area, but could impact the Savannah Metro Area. A Dense Fog Advisory could very well be needed overnight for portions of the forecast area. With fog and stratus expected to develop, temperatures across much of Southeast Georgia could bottom out around 06z then steady out or slowly rise late as the fog/stratus thicken. Have adjusted hourly temperature grids to reflect this. Otherwise, the low temperature forecast was unchanged with lows ranging from the upper 40s/near 50 across interior areas, lower-mid 50s at the coast and mid-upper 50s at the beaches. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/... Saturday: Aloft, a strong mid/upper lvl ridge of high pressure will expand across the region in advance of a low pressure trough to the west. The setup will result in temps well above normal as a deep southwest flow and ample sfc heating help produce afternoon highs in the mid/upper 70s for most areas. A few locations could reach 80 degrees near the Altamaha River in Southeast Georgia. Clouds should increase from west to east late afternoon into evening hours as deep moisture characterized by PWATs near 1.5 inches and isentropic ascent enter western zones. Showers are expected to shift into the area during early overnight hours, likely reaching the coast shortly after midnight. Overnight lows will remain mild under cloud cover ahead of the approaching cold front. In general, lows will range in the mid/upper 50s. A few locations could stay in the lower 60s along the coast and in parts of Southeast Georgia. Sunday: Showers should be ongoing while a plume of moisture characterized by PWATs near 1.5 inches persists over the Southeast near/along a cold front. At this time, precip coverage should be greatest during morning hours when forcing associated with the front coincides with the strongest upper-lvl divergence associated with the right-rear quadrant of a passing h25 jet just to our north. Showers will then taper off from northwest to southeast as dry and cooler high pressure builds over the area behind the front Sunday afternoon. Temps should peak in the mid/upper 60s for most areas before the onset of cold air advection during the afternoon/evening. A few locations could see temps in the lower 70s in Southeast Georgia. Most precip will be offshore by sunset. Temps should then cool into the low/mid 40s under clearing skies Sunday night. Monday: Dry high pressure will become centered over the Mid-Atlantic states, resulting in a light northerly wind over the Southeast United States. Temps will be noticeably cooler than the previous day despite a full day sun. In general, afternoon highs should range in the mid 50s. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Cool high pressure will persist to the northwest Tuesday through Friday while the upper pattern gradually transitions from zonal to broad troughing. Wednesday through Friday are potentially unsettled as a front develops close to the area and upper level disturbances ripple past. There are significant model differences regarding the timing of the disturbances, but Thursday into Friday currently appear most favorable for shower development. && .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/... Primary concerns: * late night/early morning fog and stratus KSAV: Conditions favor the development of fog and stratus overnight. The best parameters for dense fog look to remain just west of the terminal, but do expect vsbys to drop beginning by 08z and continuing through daybreak. Will trend vsbys and cigs lower from the 18z TAF cycle, bottoming them out below alternate minimums, but just slightly above airfield minimums. There is a real possibility that vsbys 1/4 mile or less could setting into the terminal by 10z, but confidence is not high enough just yet to include conditions that low. Conditions will rapidly improve to VFR by mid-morning. KCHS: VFR will prevail for much of the period. The bulk of the fog/stratus is expected to remain south and west of the terminal, but could briefly impact it right around sunrise. Will include a TEMPO group 11-13z for IFR cigs to account for this possibility. Extended Aviation Outlook: Flight restrictions are possible Saturday night into Sunday with showers and low clouds occurring near a passing cold front. VFR conditions will likely return at both terminals by Sunday evening, then persist through early next week. && .MARINE... Tonight: Light and variable winds late this afternoon and early evening will gradually become south to southwest overnight but speeds remain at or below 10 kt near shore and perhaps increase to 10-15 kt out closer to the warmer Gulf Stream waters. Seas near 2 ft within 20 NM and 2-3 ft further offshore. Saturday through Tuesday: South/southwest winds and seas will remain well below Small Craft Advisory levels through Saturday, but an uptick in wind speed and building seas is anticipated Saturday night into Sunday ahead of a cold front approaching the coastal waters Sunday night. Ahead of the front, the south/southwest will help advect sfc dewpts into the lower 60s over cooler waters. This could result in sea fog along nearshore waters Saturday night into Sunday until fropa occurs. Wind gusts could approach marginal Small Craft Advisory levels behind the front Sunday night into early Monday, especially in northern South Carolina waters and offshore Georgia waters. High pressure will then build over the waters with conditions remaining below Small Craft Advisory levels Monday and Tuesday next week. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
908 PM EST Fri Dec 22 2017 .UPDATE... There have finally been some reports of drizzle around metro Detroit, albeit 12 hours later than earlier expected. Sfc obs and radar suggest any drizzle will be patchy at best this evening. Temps will also hold above freezing. So no adverse impacts are expected. Slightly colder/drier air advection overnight will end any residual drizzle. Latest RAP and HRRR are a little stronger/farther north with mid level frontal forcing on the northwestern side of the precip shield expected to lift into northern Ohio overnight/Saturday morning, suggesting light snow expanding across much of metro Detroit. Given the potential instability from the sfc to 925mb portion of the frontal circulation, would not be surprised for the more active portion of the frontal boundary to remain well southeast of Se Mi. Therefore, see no reason to deviate from the current forecast attm, which restricts minor snow accums Sat morning to Monroe County. Thus, no major forecast updates will be issued this evening. Based on current temps and the extensive stratus deck, overnight mins will be raised just a couple degrees. && .PREV DISCUSSION... Issued at 549 PM EST Fri Dec 22 2017 AVIATION... Regional observations suggest ample stratus will hold through the night. There has been some weak mid level subsidence, which has resulted in some lowering of the cloud bases. This trend suggests many of the TAF sites will straddle the 1k ft threshold during the evening. Weak low level cold air advection during the night will lift the inversion base slightly, resulting in subtle rises in cloud bases heading into daybreak Sat. For DTW...There has been a rather substantial lowering of the cloud bases over the last couple of hours at metro. The closer proximity to the frontal boundary across the Ohio Valley has advected a little higher low level moisture into Detroit. This along with the weak sfc gradient has led to LIFR cigs/vsby in fog/low stratus. Low level cold air advection during the night, albeit weak, will result in a gradual improving trend to the vsby/ceiling heights. //DTW THRESHOLD PROBABILITIES... * High in ceilings below 5000 ft tonight and Saturday morning. Low Saturday afternoon and evening. * Low in ceilings and/or visibility below 200 ft/one half mile this evening. PREV DISCUSSION... Issued at 307 PM EST Fri Dec 22 2017 DISCUSSION... Energy shearing out of the southwest in advance of an approaching northern stream trough is tightening the upper mass gradient overhead this afternoon. Model progs suggest a 180kt upper jet parked directly over the central Great Lakes for the bulk of the night. Early stages of ascent are noted on IR as an increasingly organized and expanding area of cold cloud tops over the Middle MS Valley and OH Valley. Right entrance support will be outstanding, but with the lower portion of the frontal zone positioned well south of the area, the question for late tonight into early Sat will not be one of forcing, but rather the height at which the frontal zone will cease being able to produce precip. Little change from the inherited forecast in this regard. With emphasis placed on the high resolution suite, prospects appear slim for any meaningful QPF south of the Metro Area and virtually zero to the north. Still allowed for a entry level likely in Monroe County, but any snow amounts will be one half inch or less for only the southernmost areas. Transition to northwest flow as low pressure slips to the south will force a period of cold advection Saturday aftn through Saturday night. After beginning the day near -2C, 850mb temps will fall to -12C or so by early Sunday. Thus, highs Saturday will likely make it above freezing despite ample mid/high cloud debris prior to falling toward 20 degrees overnight Saturday. Attention for Sunday turns to the clipper that has been long- advertised, in one form or another, by the entirety of the long range suite. A steady trend toward the better surface response occuring east of the Appalachians has abruptly ceased and reversed today. 00z ensemble sensitivity analysis suggests energy near 150W on the upstream side of the high amplitude east ridge has been playing havoc with the ECMWF initialization and impacting downstream evolution. RAOB plots indicate multiple rounds of upper air obs have been taken over this particular portion of the Pacific over the last couple model cycles. In addition, the 12z model cycle saw improved sampling of the clipper itself. As a result, the 12z suite uniformly pulled northwest and stronger, to varying extents, with the energy of interest as it wraps into the area Sunday evening. The GEFS and GEPS have begun to lose a number of their eastern-most members at the surface while the 12z ECMWF/UKMET lead the pack, followed by the CMC, with considerably stronger solutions. Attm, it appears that a quarter inch of QPF across a strip of the CWA is more than reasonable in the 9 hour period spanning approx 18-03z Sat eve. The expectation is for this evening`s 00z NCEP guidance to make another move in this direction. Surface temps in the low 20s outside the far SE CWA suggest minimal riming while DGZ, though difficult to diagnose in non-American models, should be sufficiently deep to yield good dendrite production. Started snow ratios above climo, 14:1 with 12:1 in the far SE portion of the CWA. Areawide 1-4" on the evening of Christmas eve appearing increasingly plausible, with 4" on the higher end of the solution envelope (i.e. EC/UK) attm. Raised pops to categorical south of I-69. Christmas Day and through the upcoming week will be met with much colder temperatures behind the departing Christmas Eve system. Northwesterly flow associated with upper level longwave troughing will continue to bring colder temperatures and the potential for a few snow showers here and there for the following days. Temperatures on Monday will be on the decrease throughout the daytime hours as northwesterly winds filter in arctic air. Highs will occur in the morning before temps plummet into the teens by the evening. Low temps by Tuesday morning will be in the single digits to lower teens across the area. The rest of the week will remain relatively the same as highs only reach into the teens with lows in the single digits. Weather conditions for the week look to remain on the drier side for most of the week before chances increase again to round out the week. MARINE... Winds will veer to the south tonight into Saturday and then to the northwest into Saturday night as arctic air plunges into the Great Lakes. Another low pressure system will bring elevated winds in combination with the arctic air early next week which will result in possibility of heavy freezing spray and gale conditions in northwest flow. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ UPDATE.......SC AVIATION.....SC DISCUSSION...JVC/SP MARINE.......DG You can obtain your latest National Weather Service forecasts online at
Area Forecast Discussion
National Weather Service Fort Worth TX
827 PM CST Fri Dec 22 2017 .UPDATE... Water vapor imagery shows the potent shortwave trough moving through the Southern Plains this evening. Most of the moisture associated with this feature is quickly moving to the east with significantly drier air moving into North Texas from the west. This is reflected well in the ceiling height observations across the region with areas east of I-35 still hanging on to very low clouds and areas of light rain and drizzle. Farther to the west, cloud heights have increased to 4000 feet indicating the drier near surface air. This has also resulted in a quick end to the precipitation across the region. There is a little light wrap around precip across parts of northwest Texas and southern Oklahoma associated with strong lift near the core of the upper low, but most of this should stay to the north. For the remainder of tonight, we have lowered PoPs across all of the area and made some minor changes to cloud cover through the overnight hours. No other significant changes are needed at this time. Dunn && .AVIATION... /Issued 554 PM CST Fri Dec 22 2017/ /00Z TAFS/ Extensive IFR and MVFR cigs along with precipitation continue across North Texas this evening but conditions are expected to rapidly improve later tonight as a strong disturbance swings through the region. Latest radar imagery shows the bulk of the precipitation now east of the major airports from Dallas to Paris. Farther west, some spotty areas of light rain and drizzle remain and this will likely continue through 8-9 pm. We`ll start the TAFs off with MVFR cigs around 1500 ft which is the general prevailing condition and have a TEMPO for -RA and some lower cigs through 02Z. Much drier air will move in from the west over the next several hours and ceilings are expected to improve through the night with precipitation ending. Concerning wintry precip...a few reports of light sleet have come in from the Wichita Falls area. The more favored area for any frozen precipitation will remain well to the north of the major airports. We`ll continue to monitor this through the evening. Otherwise, VFR conditions are expected later tonight through the day Saturday. At Waco, most of the precipitation is off to the northeast. There will be some continued IFR cigs/vis over the next few hours before conditions improve later tonight. Dunn && .SHORT TERM... /Issued 340 PM CST Fri Dec 22 2017/ /Tonight/ The main challenge tonight will be precipitation cessation across North and Central TX. As we have advertised the past 24 hours, winter precipitation is unlikely across North TX tonight for a couple of reasons that will be discussed below. Otherwise, it`ll be cool tonight with drying conditions. The large swath of rain continues to lift northward across the area. There have been some embedded thunderstorms, but elevated instability remains on the lower end of the spectrum and so the coverage of storms this evening should remain very limited. The current radar presentation suggests that we may be starting to see some semblance of the mid-level dry punch northward. TTU WRF and to some degree latest iterations of the HRRR advertise that clearing will occur quite rapidly this evening. I will diminish PoPs from previous forecast, but I`ll keep a low mention for some precipitation across the area as the upper low remains to our west. At this upper low slides eastward it could spark some elevated showers. In terms of the precipitation type, I`m still confident that much of what falls will be mostly rain, despite surface temperatures nearing 32 degrees. AMDAR soundings from both D/FW and DAL Love Field Airports combined with RAP analysis indicate that temperatures aloft are still very warm (almost 50 degrees F!). IF enough low and mid-level moisture remains as the upper low scoots closer to the region, the column may cool enough such that a light winter mix of light freezing rain or sleet may occur. This would occur mainly along the Red River and across northern parts of the Big Country. This potential looks VERY LOW as it`s likely that dry air will wrap completely around the southern flank of the upper low as the deeper colder air arrives. Should winter precip occur, impacts WILL be VERY minor as recent warmth (70s for highs yesterday) combined with measured soil temperatures (OK Mesonet and here at the NWS Fort Worth/Dallas office) across the area indicate values in the mid 40s. Regardless, we will monitor trends. Overnight low temperatures should fall into the upper 20s across northern parts of the Big Country to 30s elsewhere. With regards to potential for "flash freezing" this appears unlikely due to both elevated winds, but more importantly the aformentioned soil temperatures in the 40s. I won`t completely rule out a slick bridge or overpass along far northern reaches of our CWA, however. 24-Bain && .LONG TERM... /Issued 340 PM CST Fri Dec 22 2017/ /Saturday through next week/ Saturday through Monday (Christmas Day) is expected to be quiet and dry. Nearly zonal flow is expected to persist in the wake of tonight`s shortwave passing through the region. A secondary upper level trough will swing through the Central Plains on Saturday night and Sunday, and may produce some snow in parts of Kansas, but no precipitation is expected as far south as Texas. South to west winds are expected to quickly return in the lower to mid levels of the atmosphere during the day on Saturday, and this is expected to aid in a warmer day with afternoon highs in the upper 40s to mid 50s. The sun will make a return tomorrow, but some high cloud will be present. Another cold front arrives on Sunday, and this will result in a cooler day for most of the region. The front will be moving through during the day, but temperatures are expected to fall behind the front. Therefore, our northern counties may record their high temperatures for the day in the morning with falling and/or nearly steady temperatures for the remainder of the day. Across our southern counties, temperatures will warm into the 50s before falling with the front. Despite the actual temperatures behind the front, it will feel a few degrees cooler due to strong north winds of 15-20 mph. Sunday night will be a cold night with overnight lows in the mid 20s to mid 30s. Once again, with south to west winds returning in the lower to mid levels of the atmosphere during the day on Christmas Day, and a rapid return of warm air advection, temperatures will respond with highs in the upper 40s to mid 50s. Another front will move across the region on Tuesday, and warm air advection ahead of and over the front will likely yield some light rain and showers. There isn`t any larger scale upper level forcing during this time, and lapse rates and instability look too meager to support thunder. Although both the GFS and ECMWF show this light precipitation in the Tuesday-Wednesday time frame, have kept PoPs low for now due to uncertainty in the timing of the best isentropic lift. We will be watching this time period for another chance at widespread, but light, rain for a large part of North and Central Texas. Warm temperature profiles suggest all liquid precipitation. For the remainder of the week, conditions look mostly dry with maybe low chances for rain again as we approach the weekend. JLDunn && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 33 50 37 47 31 / 30 0 5 5 0 Waco 34 53 35 52 31 / 10 0 5 5 0 Paris 33 47 35 48 28 / 60 10 5 5 0 Denton 30 49 34 46 28 / 30 0 5 5 0 McKinney 31 48 33 46 28 / 50 0 5 5 0 Dallas 33 51 38 48 31 / 40 0 5 5 0 Terrell 34 50 35 49 29 / 60 5 5 5 0 Corsicana 35 51 38 53 31 / 30 0 5 5 0 Temple 34 54 37 55 33 / 10 0 5 5 0 Mineral Wells 29 52 35 46 26 / 20 0 5 5 0 && .FWD WATCHES/WARNINGS/ADVISORIES... None. && $$
Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
849 PM CST Fri Dec 22 2017 .MESOSCALE DISCUSSION... Issued at 849 AM CST Fri Dec 22 2017 The surface analysis at 02Z indicated plentiful low level moisture advecting northward through the deep and middle south. Dew points have climbed into the lower to middle 60s across most of north Alabama, except for the counties bordering GA. A wave of low pressure was now over east central AR and will track along the frontal boundary into western and middle TN late tonight. Good convergence will remain sustained along the frontal boundary. The 00Z soundings indicated a rather strong mid level inversion around 750 mb. This is effectively limiting convective development in the warm sector as of now. Upstream, a strong upper level low over the TX panhandle (500 mb temp at AMA of -24C) was beginning to move eastward. As cold advection in mid levels pushes east into the mid south overnight, the cap should erode over the warm sector along the lower MS valley. HRRR/WRF and earlier NAM runs all indicate this. The models indicate surface based CAPE values increasing and expanding northward through MS into western AL overnight. Values of 250-500 j/kg are indicated over MS later this evening into the overnight, helping to spark off deep convection. Simulated reflectivity has been consistently forecasting the line to reach NW AL between 08-10Z, and exit our eastern counties around 14-15Z. Low level and deep layer bulk shears that are forecast are quite favorable for damaging winds and brief QLCS tornadoes. Our concern here has increased a bit due to the higher than forecast dew points. HRRR updraft helicity forecasts indicate this as well over far NW AL into middle and southern TN late tonight. We have mentioned the potential for a brief tornado in our HWO and new graphics. && .NEAR TERM...(Tonight) Issued at 628 PM CST Fri Dec 22 2017 Ceilings are lowering and areas of drizzle are developing at many locations, especially south of the TN river. Southerly flow was advecting surface dew points into the lower 60s. Meanwhile, the main corridor of heavy rain remains across western TN into AR. This should remain in this orientation for several more hours before a surface wave in southern AR advances northeast along the front the cold front advances northeast along the front by around 06Z. Then the QLCS and front should make progress eastward into north AL and southern middle TN. The latest HRRR runs have indicated the line may enter NW AL by 07-08Z, then to near Tullahoma-Athens-Moulton around 12Z. Low level shear will be quite strong, with 2km bulk shear values of 55kt forecast at a rather favorable angle to the QLCS. This may promote the potential for bowing segments and mesovortices. Thus, will continue to mention the potential for damaging wind in our HWO. Will evaluate the severe potential further after the 00Z data arrives. .SHORT TERM...(Saturday through Sunday) Issued at 115 PM CST Fri Dec 22 2017 The cold front will approach the region rather quickly from west to east on Saturday as the progressive upper trough ejects quickly out of the Plains. Fropa will be mid morning across the Shoals and perhaps early afternoon across NE Alabama. Despite strong mass convergence/lift along the front and a potent mid level jet the precipitation amounts with the front will be tempered by the speed of the system. Cannot rule out an isolated strong/severe storm given the kinematic forcing and mid level lapse rates, but again the window for occurrence is rather narrow. The other sensible weather impact of note will be the gradient winds. Given the strength of the low level jet, have bumped gusts up to around 30 mph or just below advisory levels. Precipitation will clear quickly from west to east, and honestly the current forecast may be too generous keeping PoPs in through the early afternoon. Cold air advection will begin in earnest during the afternoon and evening and will hold low clouds in longer than guidance suggests (given the climatology of such systems). Sunday looks somewhat interesting as well. The upper level trough axis will be approaching from the west during the day. Despite weak to barely discernible lift this far south we may see enough lower tropospheric instability for extremely low topped showers/wraparound. Cannot rule out the upslope contribution in our eastern counties and that is where we will place PoPs for now. Given the profile precipitation should fall as rain during the daylight hours but will need to monitor model trends. Either way, Sunday is going be a rather raw Christmas Eve around the Valley. .LONG TERM...(Sunday night through Thursday) Issued at 244 PM CST Fri Dec 22 2017 The extended forecast will start off on a chilly Christmas morning with temps in the upper 20s and wind chills in the teens/lower 20s. It will warm up into the lower 40s by midday. The week will start off with sfc high pressure across the region and zonal flow aloft. On Tuesday, as the sfc high shifts eastward, a weak front will push southward through the TN Valley but is not expected to develop any precip. Through the rest of the forecast period, the models are not only in a disagreement but keep flipping on what will happen. They do agree that a sfc high in the Northern Plains will build into the Great Lakes as a sfc wave develops in the northern Gulf. The ECMWF and GFS has flipped with the coverage of precip they are brining in Tues night through Thurs. The ECMWF now starts to bring in precip from the south Tuesday night as the sfc high track stays farther north and there are southerly 850mb winds enhancing lift. With temps hovering around freezing Tuesday night, can`t rule out a mix of rain/snow but will keep that as slight chance for now and will definitely keep accumulations out. Kept a slight chance of rain in through Wed with the sfc wave still to our south. Not to mention as a middle ground of opposing model solutions as the GFS keeps the precip confined to the Gulf Coast which is opposite of yesterday`s run. Kept in a chance of rain on Thursday as a shortwave moves into the region. Temps will be in the mid 40s on Wed and Thurs with overnight lows in the low/mid 30s. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 452 PM CST Fri Dec 22 2017 Ceilings of 015-020agl (MVFR) will likely lower back into the 010-015agl range early this evening (by ~02Z). Then as southerly flow increases to 12-16kt with gusts of 24-26kt by 08Z, expect ceilings to lower to ~007agl for a few hours. A line of heavy showers and possibly a thunderstorm will arrive between 10-13Z at KMSL and 12-15Z at KHSV. This line will produce a period of +RA and vsbys down to 3sm or below briefly and brief wind gusts up to 40kt. Behind this line, winds will shift abruptly to westerly then northwesterly with continued gusts over 20kt expected. Ceilings will remain in the 010-020agl range for the balance of the period with isolated to scattered light showers. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ MESOSCALE...17 NEAR TERM...17 SHORT TERM...15 LONG TERM...JMS AVIATION...17 For more information please visit our website at
Area Forecast Discussion
National Weather Service Lincoln IL
921 PM CST Fri Dec 22 2017 .UPDATE... Issued at 910 PM CST Fri Dec 22 2017 Low pressure in southern Arkansas will expand and advance to the northeast overnight, reaching Tennessee by 07z-08z. As the low center progresses along that path, rain showers will expand northward into our southern counties. There are differences in the latest models about precip type, with the RAP leaning more towards rain up to Mattoon, with a couple tenths of snow late tonight before precip ends. Just north of there, the RAP indicates a narrow band of 1-1.5 inches of snow from Decatur to Champaign. The warm ground will counteract that much accumulation, but our current forecast has mainly less than a half inch of snow in that band. The GFS and NAM also show a band of snow, slightly higher than our forecast snow. Forecast soundings show the potential for a little sleet to mix in as well, which would reduce snow amounts. Have increased snow amounts a little in the DEC to CMI corridor, to trend up, but the first snows of the season can have a harder time accumulating. Have kept our snow amounts just under an inch in that area, with less than a half inch south of Mattoon. Precip should begin to shut down quickly tomorrow morning, as the low pulls away to the east and drier air is pulled into Illinois from the north. Low temps tonight should be held a little warmer due to persistent cloud cover. SE areas look to drop into the upper 30s, with some low to mid 20s possible towards Galesburg. Updates this evening were to the PoP/Weather grids, along with QPF and snow amounts. The latest forecast info will be available shortly. && .SHORT TERM...(This evening through Saturday) ISSUED AT 140 PM CST Fri Dec 22 2017 Large rain shield advancing northeast toward the Ohio River early this afternoon. Expect more of a push northeast this evening, as low pressure rides northeast out of Arkansas. This should be arriving south of I-70 early to mid evening, with a northwest pivot in the precipitation shield with time. How far north it makes it is a bit of a question, with the high-res models up to near a Champaign-Springfield line and the ECMWF on the higher range near Peoria. Have not changed too much from earlier forecasts in that regard, aside from adjusting the hourly grid trends. Rain to snow transition on the northwest edge should begin around midnight and work southeastward, though the extreme southeast CWA should see the changeover Saturday morning. Snow amounts should generally be a half inch or less. Lingering precipitation will exit toward midday, as a fast moving upper wave sweeps through. .LONG TERM...(Saturday night through Friday) ISSUED AT 140 PM CST Fri Dec 22 2017 Odds of a White Christmas continue to improve, with all the synoptic models continuing to show a decent streak of snow racing across the mid-Mississippi Valley. Will increase snow totals into the 1 to 2 inch range over most of the forecast area for Sunday, though I-70 southward will have lower totals with more of a melting factor. Still looks like the western CWA will see the snow quickly end early afternoon, but have lingered 50-60% PoP`s in the far east until late afternoon. Southward push of Arctic air begins in full force Monday night and Tuesday, aided by the fresh snow cover. Highs over the northern CWA likely to stay in the teens Tuesday, though the far southeast may still manage to reach freezing. Have trended significantly colder with lows Tuesday night, single digits most places, though it should be noted the ECMWF MOS guidance brings lows below zero. Some northward retraction in the cold air mass will occur later in the week, with the next surge toward Friday- Saturday. Some questions continue with the strength of a shortwave arriving on Thursday from the northwest, but there is enough model agreement for a healthy boost in snow chances. Similar to the Sunday system, no real moisture advection from the south to boost amounts, but snow totals may be similar for the late week system. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 557 PM CST Fri Dec 22 2017 MVFR clouds will prevail tonight through mid-morning tomorrow, as low pressure progresses from Arkansas to Tennessee. The precipitation shield will advance northward toward DEC and CMI after midnight, with light rain initially, then transitioning to light snow from NW to SE toward sunrise. There could be some light snow accumulation of a tenth or two at DEC and CMI, but mainly on grassy surfaces and not much on travel surfaces. Precipitation will shut down by sunrise at DEC and CMI, with cloud heights improving to VFR by mid to late morning. During the afternoon, skies should clear out from NW to SE as dry air pushes into Illinois. Winds look to remain N-NW throughout the 00z TAF valid period, with speeds prevailing below 10kt. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Shimon SHORT TERM...Geelhart LONG TERM...Geelhart AVIATION...Shimon
Area Forecast Discussion
National Weather Service Northern Indiana
1041 PM EST Fri Dec 22 2017 .SYNOPSIS... Issued at 655 PM EST Fri Dec 22 2017 Light snow is expected for areas primarily along and south of Highway 24 late tonight into Saturday morning with accumulations around an inch, possibly two inches in spots. More widespread snow is then expected on Christmas Eve with 2 to 4 inches for the entire area, with higher accumulations closer to Lake Michigan. Much colder air will then arrive for the middle of next week with highs only into the teens and lows in the single digits. Periodic lake effect snow will also be possible through much of next week. && .UPDATE... Issued at 1038 PM EST Fri Dec 22 2017 Signficant update with respect to latest high-res model trends, snow/liquid ratios, top/down thermodynamics. HRRR continues northward trend through the late afternoon/evening hours with hard blend towards lastest consshort. Primary influence in KFWA/KAOH markets, though some concern farthern north lower prob light snow/small chance of zl due to shallow saturated depth/failed nucleation could create some isolated early am slick spots south central Lower Michigan into greater terrain areas of far northeast IN around daybreak. && .SHORT TERM...(This Evening through Saturday) Issued at 317 PM EST Fri Dec 22 2017 Drizzle will linger over SE zones through the afternoon into early evening as nearly stationary boundary slowly gets pushed eastward by our next system. Drying out this evening for most areas before the next wave currently over the southern plains moves north and east into the area after midnight Fri into Sat morning. Main plume of moisture will remain south of our CWA but northern edge of precip will clip areas in our SE. Recent HIRES guidance is keeping areas north of US 24 dry with a tight gradient south. Precip starts out as rain then transitions to snow as winds shifts to more northerly bringing in cold air dropping temps below freezing Sat morning. Not expecting much snow accumulation (less than 1 inch) due to warm afternoon Fri temps near 50F. && .LONG TERM...(Saturday Night through Friday) Issued at 317 PM EST Fri Dec 22 2017 Another shortwave ejects eastward Sunday into Sunday night through the region. Cold temps in place will lead to all precip falling as snow. Compared to the previous system, this one has stronger upper level forcing associated with it. Positive vorticity advection resulting in strong omega values over much of the CWA will lead to widespread snowfall starting 12Z Sunday morning. Expected snowfall accumulations 2-3 inches area wide with heaviest amounts south of US 24. WNW flow on backend of system will initiate LES to form downwind of the lake and could linger throughout Christmas day. Additional 1 to 2 inches possible in far NW IN and SW lower MI. Coldest air mass of the season intrudes the region by Christmas evening as lows fall into the teens. Due to snow pack from Sunday and clearing out overnight Monday had to cut temps considerably from the blend. Single digit lows expected Monday night and Tuesday night with wind chills Tuesday night dipping below 0F across much of the area. Several chances of LES Monday through Thursday with the best chance Tuesday as another shortwave passes quickly through the area. Another synoptic system possible by late next week but confidence is low because of the lack in agreement between model guidance. Below normal temps stick around for the entire period but with some moderation by late week compared to early in the week. && .AVIATION...(For the 00Z TAFS through 00Z Saturday Evening) Issued at 659 PM EST Fri Dec 22 2017 Small mesoscale feature still northwest of KFWA and will maintain lower IFR ceilings in light drizzle for next couple of hours. Thereafter, modest improvement to above fueling/alternate criteria until daybreak system moving up the Ohio Valley with finer high resolution data indicating secondary/northern focused enhancement with mid level deformation axis and I295K to briefly tap into 3.5-4 g/kg moisture about 12 UTC, will provide lower LIFR conditions within best potential vis/cig reductions in snowfall from 11-14 UTC for planning purposes, later forecasts to better ascertain confidence as KFWA likely on northern fringe worst conditions. A bit easier at KSBN, though with fueling/alternate requirements likely for large portion of forecast period beneath persistent inversion. Gradual whittling of moisture depth and only marginal lake enhancement/thermal differentials should allow return to VFR by about midday, and later at KFWA in evening/towards end of forecast period. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...Small Craft Advisory from 4 AM to 7 PM EST Saturday for LMZ043- 046. && $$ UPDATE...Murphy SYNOPSIS...Murphy SHORT TERM...Heidelberger LONG TERM...Heidelberger AVIATION...Murphy Visit us at Follow us on Facebook...Twitter...and YouTube at:
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
929 PM CST Fri Dec 22 2017 .UPDATE... Issued at 927 PM CST Fri Dec 22 2017 Rain has overspread much of the CWA south of I-70. The regional radar mosaic is showing a sharp gradient on the north side of the precipitation shield which currently extends from southwest Illinois to central Missouri southwestward into northern Oklahoma. Expect this precipitation to continue through the night as shortwave trough currently over western Kansas/Oklahoma races northeast and weakens overnight. Low air cold air advection continues to move into the area and RAP soundings are showing low level thermal profiles falling below freezing across the area overnight. Upstream obs at Lake of Ozarks and Lebanon have turned over to snow, so going forecast of rain changing to snow still looks on track. Have not made to much deviations to going forecast amounts through tomorrow morning. Britt && .SHORT TERM... (Through Late Saturday Afternoon) Issued at 221 PM CST Fri Dec 22 2017 First in a series of shortwaves over TX/OK Panhandles, lifting northeast towards mid Mississippi River Valley as of 19z. So overrunning precipitation has developed over far southern portions of forecast area. Even enough instability that there is some isolated thunder with it. Will see precipitation increase in coverage mainly along and south of I-70 corridor this evening as main shortwave finally lifts out towards region. As the precipitation shield spreads north, it will encounter a colder airmass both at the surface and aloft. So will see the rain mix with snow this evening, then turn to all snow after 06z from northwest to southeast. Could see decent snowfall rates for a few hours during this period, mainly along the I-44 corridor in Missouri. So 1 to 2 inches of snow expected with locally higher amounts possible in this area. With ground temperatures still quite warm, in the low to mid 40s, much of the snow will likely melt on contact, except in areas where the snowfall rates are high enough to overcome this issue. Precipitation to taper off by 18z Saturday as system exits region. Will have partly sunny conditions Saturday afternoon with highs in the low 30s to low 40s. Byrd .LONG TERM... (Saturday Night through Next Friday) Issued at 221 PM CST Fri Dec 22 2017 Main focus of the long term is a few chances of snow through mid week next week. Saturday morning snow will be on the wane as the short wave quickly departs the region. H5 flow flattens a bit ahead of the next short wave approaching from the Northern Plains. Cold hair behind the larger scale H5 low will keep Saturday highs from just above freezing in the I-75 area to the low 40s elsewhere. Next shot of snow will be on Sunday morning as another short wave passes through the area. This will be a fast moving wave, aided by a stronger upstream jet. Light snow amounts are expected, mostly around a 1/2 inch in the STL with around 2 inches in the Quincy area. There are a few model differences, with the GFS/ECM slightly farther south with snow than the NAM and the bulk of the ensembles. Differences seem mostly due to a farther south position of the trough and associated short wave and frontogenesis. That said, there still has been a very small and gradual shift south with the southern edge of the snow area which at this time brings it down to the I-70 corridor. Expect snow to start in the pre-dawn hours near Quincy then into the St. Louis and Columbia areas by around dawn. Snow is expected to come to an end by sunset, then skies will clear out allowing for cold lows in the teens as people wake up on Christmas morning. From Christmas day through Wednesday, no precipitation is expected. Cold temps will hang on through the week next week with highs not making it out of the 20s for most of the area on Tues/Wed/Thurs. GFS is bringing in another round of light snow on Thursday but there are differences between that and the less progressive ECM so amounts and coverage are highly uncertain at this time. Sally && .AVIATION... (For the 00z TAFs through 00z Saturday Evening) Issued at 617 PM CST Fri Dec 22 2017 MVFR conditions are expected to continue through the evening hours at all of the terminals. A mix of rain and snow will move into the Columbia and St. Louis area terminals by mid evening that will switch over to all snow after 06Z. IFR conditions can be expected at the St. Louis terminals between 08-12Z when the snow will likely be the heaviest. The snow is expected to move out of the area after 12Z tomorrow with quick improvements in ceilings and visibilities. Soil temperatures are still well into the 40s, so runways will likely be wet except where snowfall rates are high enough to cause accumulations on runways. Winds will be out of the northwest at 10 knots or less through the period. SPECIFICS FOR KSTL: MVFR ceilings are expected to continue through the evening hours. Rain will move into the area by mid-evening, with rain changing to all snow between 06-08Z. IFR conditions are expected with snow accumulations between 08-12Z. Soil temperatures are still well into the 40s, so runways will likely be wet except if snowfall rates are high enough to cause accumulations on the runways. The snow will clear out quickly after 12Z, as will the MVFR conditions. Dry and VFR conditions are expect most of Saturday. Winds will be out of the northwest at 10KT or less through the period. Britt && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX
Area Forecast Discussion
National Weather Service Omaha/Valley NE
923 PM CST Fri Dec 22 2017 .UPDATE... Issued at 907 PM CST Fri Dec 22 2017 ...The odds for a White Christmas appear to be increasing... For this update, trimmed the arrival time of light snow along the NE/SD border region by a few hours later tonight. Latest HRRR/RAP/ESRL HRRR all suggest that the snow in southwest SD may be a little slower than previously thought, so adjusted timing until after 12z in that area. Also increased an area of MVFR clouds in northeast NE tonight. Latest 00Z Nam still suggesting snow moving in with a couple of weak waves aloft that move through the area Saturday. The first wave will bring snow to the area through the morning into the early afternoon. This first area is mostly north of I-80 and will likely be an inch or less. This first area tends to dissipate through the late afternoon. The second round of snow sets up through the evening and overnight, then pushes east of the area by 12-15z on Sunday. Winds will not be especially strong either. Temperatures will remain quite cold, with snow ratios ranging 17-21:1 for this event. Still looking at 1 to 3" total, but made some minor tweaks on QPF Saturday night to nudge northward the 1-2" snow line just a little closer to Omaha based on recent model blends. Given the high snow ratios, would not be surprised to see a 4" amount somewhere in southeast NE or southwest IA south of I-80. Obviously need to see the full suite of 00z model data to nudge amounts up. && .SHORT TERM...(Tonight through Monday) Issued at 320 PM CST Fri Dec 22 2017 Forecast concerns in the short term will be increasing clouds and temperatures...then development of light snow and flurries late tonight through Saturday night. The cold front was moving into northeast Nebraska with temperatures in the 20s/30s and dewpoints in the 20s ahead of it and temperatures in the teens and dewpoints in the single digits and teens behind it. Visible satellite imagery and obs showed quite a few MVFR ceilings with some flurries behind the front along with a few breaks showing up. The RAP/HRRR are trending toward cooler temperatures compared to the blend. Although we are looking at increasing clouds, did go with colder temperatures with most lows between 8 and 16 above. Upper level divergence increases tonight and continues Saturday as a couple of shortwaves within the large mid tropospheric trough across much of the U.S. impact the area. -10 deg h85 air arrives in northeast Nebraska after 03-06Z. Moisture increasing from the west combined with this lead shortwave should spread light snow and flurries from northwest to southeast across southwest South Dakota into central Nebraska by 12Z. The NAM is farther north and more aggressive with the light snow during the morning, however the RAP/HRRR are still more in line with the GFS/EC. Until there is more to support this northward saturation, will keep the current trend going. That said, with temperatures this will be easy to get light snow and flurries. Accumulating light snow ramps up during the afternoon and overnight hours. We currently have half an inch to 2 and a half inches over parts of east central and southeast Nebraska into southwest Iowa. Of note, the UKMet and the EC are a little farther north with the track of the storm system. The snow moves out for Sunday with additional light snow Monday afternoon. Below normal temperatures continue with highs in the teens and 20s and lows in the teens. .LONG TERM...(Monday night through Friday) Issued at 320 PM CST Fri Dec 22 2017 The light snow continues across parts of the area Monday night. The GFS/EC have much colder temperatures moving in Monday night with lows closer to zero and highs Tuesday are only in the teens. With the cold pattern in place, additional shots of light snow continue Wednesday into Friday. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 525 PM CST Fri Dec 22 2017 VFR conditions through most of the period. Light snow chances begin to increase at KOFK by 14-15z, KLNK by 17-19z, and KOMA 19-21z. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ UPDATE...DeWald SHORT TERM...Zapotocny LONG TERM...Zapotocny AVIATION...DeWald
Area Forecast Discussion
National Weather Service Mount Holly NJ
954 PM EST Fri Dec 22 2017 .SYNOPSIS... Low pressure from the Tennessee River Valley will move northeast overnight and Saturday, reaching the New England coast late in the day. A strong cold front associated with this low will move through the area and off the coast Saturday night. High pressure will then build in behind this front on Christmas Eve before yet another low moves northeast just off the coast early Christmas morning. Cold high pressure is then expected for a good portion of next week. A coastal storm is possible next weekend. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 930 pm update: No updates to the forecast were necessary. 630 pm update: Needed to update dew points across the area, as they were generally too high by 3-7 degrees. Temperatures were mostly OK, though a little too warm north of Delaware Bay. I modified PoPs a little bit based on latest short-term/hi-res guidance, but these changes were minor for the most part. A review of the latest HRRR, 18Z NAM Nest, and some of the coarser 18Z guidance suggests lingering uncertainty with the precipitation evolution overnight. Although the consensus is that the heaviest/most widespread rain will be north of the Mason-Dixon Line, the HRRR in particular is displaced about 50 miles southward and also quite a bit faster with getting precipitation into the area. As such, this involved increasing PoPs in the south and ramping up the start time a little bit. There is a possibility of two waves of precipitation. The first will be fairly light and would occur late evening into the early morning hours. The second would be the start of the main show, with widespread light/moderate rain entering the CWA late tonight. PoPs really ramp up 09Z onward for this second round. Previous discussion... Developing warm front currently across the area well ahead of a low pressure system across the midwest. As a result, quite the temperature contrast with temperatures ranging from the upper 50s over southern Delaware to the 30s over the southern Poconos. As expected, the precip associated with a lead disturbance moving NE along the front has stayed to our north though low and mid level clouds have brought mainly cloudy skies. Heading through the late afternoon into this evening, not looking at things changing to much...a few light sprinkles or showers will be possible both across the far north through the southern Poconos as well as right along the New Jersey coast due to marine moisture. Some of the forecast guidance continues to hint at some fog developing right along the NJ coast this evening however not confident in this as flow will be more from the S/SW. Most of the evening should continue to be mainly dry though toward 6z there may be just enough moisture and lift with weak PVA to bring in a few light showers or sprinkles. Beyond this time expect rain developing overnight as the low begins to get better organized across the Ohio Valley in response to stronger forcing aloft. The steadiest rain will be mainly along and north of where the warm front will be setting up so looking at areas from around Philadelphia and Trenton northward. Temps may fall a bit this evening then should hold steady or rise overnight in response to strengthening warm advection. Temperatures will be mild enough for all precip to fall as rain. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... For Saturday, low pressure moves north and east through the day from the Ohio Valley through PA and NY toward New England...passing near or just north of the area. Rain will continue into the morning...mainly for the aformentioned areas along and north of the warm front where it could fall moderate at times as a 60 knot low level jet advects in PWATs in the 1.25 to 1.5 inch range. There may be a break in the precip around central NJ and SE PA around midday as the warm front lifts north before rain and showers return by late day ahead of the system`s cold front. In fact much of the Delmarva and southern New Jersey may not see much precip until the cold front arrives late day Saturday. Temperatures will be quite mild due to the strong SW flow with highs in the low 60s for the Delmarva and southern New Jersey with 50s for the remainder of the region except 40s across the southern Poconos and northern New Jersey. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... A broad mid-level trough over northern Canada is expected to dig further south into the continental U.S. early in the weekend before migrating slightly poleward early next week before then digging south once again next weekend. As a consequence of this pattern, the mid-level southwesterly flow pattern will continue into early Sunday, before veering to a zonal mode late Monday through most of the upcoming week. At the surface, a strong cold front will move off the coast early Saturday night, followed by high pressure moving northeast from the Ohio River Valley. Two developing low pressure systems, one moving with a mid-level trough, and one forming along a stalled frontal boundary just off the coast, are expected to merge by the time both reach the New England coast early Christmas morning. Temperatures with these systems will be cold enough for snow over inland sections (along and west of I-95), but rain or a mixture of rain and snow is more likely near the coast. Models are in somewhat good agreement in assigning around one-quarter inch or less of precipitation with these systems as they move through, which could equate to one to three inches of snow, especially north and west of the I-95 and I- 195 corridors. Blustery/windy conditions are expected after the low pressure systems move to our north on Christmas day, with gusts in the 30 to 40 mph range into the evening hours, with a gradual step-down into Tuesday morning. High pressure then building in from the upper Great Lakes will produce a northwesterly flow at the surface, with occasional bouts of snow flurries through the remainder of the week. After Christmas Day, the most noticeable sensible weather feature will be the below normal temperatures which are expected to persist for a good part of the week. Normally a mid-level zonal flow pattern might result in somewhat moderate temperature regime, but streamlines with next week`s expected pattern originate in the polar regions of the far north, with some moderation as the air makes its way here. && .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR through the evening with slow deterioration to MVFR as CIGs descend and rain begins to enter the region near/after 06Z. VSBYs may start to lower as well near daybreak as rain becomes steadier. Light/variable winds. Medium confidence in CIGs/VSBYs; high confidence in winds. Saturday...Sub-VFR likely most of the day with widespread rain, especially north of the Mason-Dixon Line. A cold front will enter the region during the afternoon, and this could generate some isolated convection within the steadier rain, with perhaps a lightning strike or two near/south of PHL. In advance of the front, winds will become easterly and veer to southerly, generally near/below 10 kts. However, stronger winds/gusts will likely occur at MIV/ACY. Near/after frontal passage (generally in the 18Z to 00Z time window), winds will veer to southwest or west and could begin to gust to around 20 kts or so. Medium confidence in general evolution of the rain/clouds/winds, but low confidence in exact timing. Outlook... Saturday evening...Sub-VFR probable with periods of rain or snow showers. There is at least a slight chance of a lightning strike or two during the late afternoon and evening hours generally south of the Mason-Dixon Line. Winds veering from south to west through the period, with speeds 5-15 kts and higher gusts, especially near the coast. High confidence. Saturday night and Sunday...Improvement to VFR expected. Northwest winds 5 to 15 kts with higher gusts Saturday night and Sunday morning becoming lighter and more northeasterly Sunday afternoon. Medium confidence. Sunday night...Rapid deterioration to MVFR/IFR with a chance of rain and/or snow. Winds changing from east to north to northwest and becoming strong near daybreak (10 to 20 kts with higher gusts). Medium confidence. Monday...Improvement to VFR, but very strong west/northwest winds likely (speeds 15 to 25 kts with gusts 30 to 40 kts possible). High confidence. Monday night through Wednesday...Mainly VFR, though CIGs around 5000 feet may occur. Flurries possible with a northwest flow. Light west winds. Low confidence. && .MARINE... Conditions will be below SCA tonight with SW winds around 5 to 10 knots and seas around 2 to 3 feet, except 1 to 2 feet over Delaware Bay. There could also be some light fog or drizzle around. For Saturday, conditions ramp up to SCA over the coastal waters of New Jersey with winds increasing to 20 to 25 knots with gusts to around 30 knots. Also expect periods of rain in addition to building seas. Outlook... Saturday night...Small craft advisory continues for the Atlantic waters this period as strong southerly/southwesterly winds and building seas occur in advance of a system moving through the area. Rain with an isolated storm likely, especially Saturday night, with visibility restrictions possible. Conditions should remain sub- advisory on Delaware Bay. Sunday...Sub-advisory conditions and fair weather expected. Sunday night...Conditions rapidly deteriorate as rain and/or snow develops (with visibility restrictions possible) and winds becoming west-northwest, potentially reaching gale-force by daybreak. Monday...Gale-force west/northwest winds likely. Precip should rapidly end during the morning. Monday night...Small craft advisory conditions likely as Gale conditions wane. Tuesday and Wednesday...Sub-advisory conditions and mainly fair weather expected. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 7 AM Saturday to 6 AM EST Sunday for ANZ452>455. Small Craft Advisory from 10 AM Saturday to 6 AM EST Sunday for ANZ450-451. && $$ Synopsis...Miketta Near Term...CMS/Fitzsimmons Short Term...Fitzsimmons Long Term...Miketta Aviation...CMS/Miketta Marine...Fitzsimmons/Miketta
Area Forecast Discussion
National Weather Service Blacksburg VA
850 PM EST Fri Dec 22 2017 .SYNOPSIS... High pressure will move east this evening and push offshore in the Atlantic ocean tonight. An elongated area of low pressure from the Great Lakes to the Southern Plains will move east through Saturday, pushing a strong cold front through the region. A large high pressure system will much colder air will cover much of the eastern United States Sunday and Monday. && .NEAR TERM /THROUGH SATURDAY/... As of 845 PM EST Friday... Ongoing gridded forecast still appears to be on track, and see no need to make any significant changes at the present time other than to infuse some additional spacial specificity based on latest available high-resolution model projections, and upstream surface, satellite, and radar observations. Best area of isentropic lift maximized in 850-600 millibar layer has now begun to lift north of much of the Blacksburg forecast area excluding areas along and north of the I-64 corridor. Best Theta-e advection and broad upward vertical motion fields will continue to lift north for the rest of the night, so gradual reduction of precipitation threat from current widespread to more of a scattered nature still seems appropriate. Spotty light warm advection showers could still impinge as far east as portions of the Piedmont near the foothills, but will remain light and widely scattered. Exception will be across the eastern flanks of the Blue Ridge, where localized warm moist upsloping will continue to help wring out a strip of light rain/drizzle through much of the night. Abundant cloud cover and increasing winds aloft should help to hold temperatures to well above normal values for this time of year, mainly in the 40s, and not much lower than current readings. Previous discussion as of 644 PM EST Friday... No major changes needed to the going forecast. METARs and composite radar mosaic indicate lower-level warm advection- driven rains has begun to move into the Mountain Empire in far southwest Virginia and into southeast West Virginia. Though radar is indicating precipitation further east/northeast, sub- cloud air mass remains too dry to support measurable precip with dewpoint depressions being still too high. Recent near-term guidance keeps any measurable rain confined to areas along or west/northwest of I-81 through midnight, while lifting the rain shield more northward than eastward later in the overnight hours. Official forecast does show a small decrease in PoPs, keeping to Chance-level, in the overnight for areas in the far west. Otherwise no other changes needed attm. Previous discussion issued at 303 PM follows... High pressure gradually moves offshore this evening into tonight. Surface cold front and low pressure will approach our region from the west tonight. Moisture will slowly increase this afternoon into tonight as the low pressure center lifts northeast. Regional WSR-88d images showed a large area of rain to our west across Kentucky and Tennessee. This rain will advance northeast tonight into our region. This rain will be hindered by the dry airmass across our region. Shaped the evening pops towards a blend of HRRR and HiResW-ARW-East, then utilized a blend of continuity and Superblend for tonight. The northwest to west portions of the forecast area have the best chance for rain, then the potential tapers off as one heads southeast. 850MB winds continue to increase from the southwest overnight. Kept wind speed up overnight into Saturday where stronger southeast downslope winds are favored from southeast West Virginia into Tazewell County. A few of the highest peaks may approach wind advisory levels Saturday morning, however decided to hold off on any wind advisories because of the limited coverage which is typical with a warm sector LLJ event in the mountains. Used an non-diurnal temperatures curve tonight because of winds and Warm advection. Low temperatures overnight will vary from the mid 40s in the northern mountains to the lower 50s across the western mountains. Surface dew points in the mid 40s to lower 50s and all the cloud cover will limit drop in temperatures tonight. Lows may be in the ridges. The lows are tricky because the actual minimum may be reach during the evening with steady or slowly rising temperatures overnight. Surface low pressure and its accompanied cold front will cross our area on Saturday into Saturday evening, bringing much needed rain to the region. Widespread rain will spread into the western parts of the county forecast area during the afternoon, then move east into the Piedmont. The Day Two Convective Outlook indicated the chance for some elevated convection with a general thunderstorm area. However, the instability looked to low to mention thunderstorms at this time. High temperatures Saturday will vary from the lower 50s in northwest mountains in Greenbrier county to the mid and upper 60s in the Piedmont. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... As of 250 PM EST Friday... The cold front and associated rain showers will move out of the area and over the coastal piedmont early Saturday evening. Cold northwest flow and residual low level moisture will keep low clouds and the chance for light rain/snow along western slopes of southeast West Virginia and extreme southwestern Virginia into the early morning hours Sunday. With limited moisture, we are only expected a dusting to maybe half an inch for elevations above 3500ft in Western Greenbrier. Behind the front, cool high pressure will wedge south into the Carolinas. The colder air is lagging behind and will not enter the area until Sunday. Saturday night temperatures will remain warmer than normal with readings in the mid to upper 30s across the mountains and low to mid 40s in the foothills and piedmont counties. Temperatures will slowly rise during the day Sunday, but with cool northeast flow and a blanket of clouds, diurnal temperatures ranges may only be on the order of 10F. High temperatures Sunday may warm into the 40s across the mountains and north of hwy 460 in the piedmont to lower 50s across Southside VA and northwestern North Carolina piedmont. There is a chance that temperatures could be cooler as some models (GFS/NAM) are indicating light precipitation falling into the wedge during the day Sunday. Also on Sunday, an upper level trough will move over the upper Mississippi Valley with a leading cold front over the Ohio Valley. Ahead of the front is an inverted trough and a thermal ridge. Couple these two features with low level convergence over the mountains will likely bring light rain showers across the mountains in the afternoon. If temperatures are allowed to cool or stay cold through the afternoon, light accumulating snow is possible. This light precipitation will be more focused over the mountains, but with easterly upslope, the foothills may also get in on some precipitation action. Precipitation will taper off through the evening and be more directed on western slopes by Christmas morning. Snow accumulations may range from a dusting to half inch across mountain valleys to an inch or so along higher ridges. Western Greenbrier may see up to 2 inches Sunday afternoon into Monday morning. The upper level trough will push the cold front through the area Sunday evening, removing the wedge, but will bring very cold temperatures into the region for Christmas. Morning lows will range from the low to mid 20s west of the Blue Ridge to near 30F east. Temperatures will warm to near freezing in the west and near 40F in the east Christmas day. However, pressure rises and a 40kts low level jet will make for windy conditions with wind chills values in the upper teens to lower 20s in the mountains and lower 30s east. Can not rule out a few mountain flurries for Christmas morning, but overall a dry day. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... As of 250 PM EST Friday... High pressure will move over the region Tuesday and Wednesday and with a blanket of high clouds, temperatures may only warm into the upper 30s to mid 40s. These temperatures are around 5F cooler than normal. A dry back door front will move quietly over the area Wednesday night, then another high pressure system will wedge south into the Carolinas on Thursday. With a re-enforcing shot of cold air, Thursday afternoon temperatures may not make it out of the 30s. Thursday night into Friday is when the weather could get interesting. Models are advertising a Miller B storm pattern. Models are generating a surface low pressure that will track along the western side of the wedge (TN-OH) Thursday night into Friday. As the upper level trough moves east of the Great Lakes, a secondary surface low may form in the vicinity of the southeast coast Friday. The first low will give the area moisture for precipitation. The second will pull moisture away from the area. So there are two main questions that will need to be answered over the next several days. The first is regarding precipitation type. With the first wave tracking west of the area, a warm nose may introduce a wintery mix of snow, rain and/or freezing rain. The second question to this scenario will deal with liquid precipitation amounts and that will likely be dependent on which wave becomes the parent low. The 12Z GFS, which is usually bullish on precipitation amounts only has a tenth to two tenth of liquid for Thursday night into Friday. If this is an all snow event, we may only see a couple of inches. However, if it turns out to be more of a freezing rain event, even light amounts will increase the impact on the area. One more thing to keep in mind, this forecast period is 7 days out. We will have a better handle on this potential storm early next week, if the models remain constant. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... As of 644 PM EST Friday... Warm front continues to steadily progress northward across the TAFs overnight. Worst aviation conditions through 12z mainly at Bluefield with MVFR/IFR ceilings and VFR-MVFR showers, though brief intervals of MVFR possible at Lewisburg and Blacksburg. Will also begin to see worsening conditions along the southern Blue Ridge later this evening due to southerly upslope leading to potential development of fog/stratus. Appears showers confined to areas west of the Blue Ridge through 08z before lifting north/northwest with VCSH indicated. Otherwise looking at VFR conditions for the rest of the TAFs through 12z. Toward early morning, southwesterly low- level jet becomes enhanced contributing to low-level wind shear and turbulence in/around the Blue Ridge. Surface winds should experience a modest veer to south around 4-8 kts. VCSH with VFR/MVFR ceilings and breezy southwest winds should be the rule for early on Saturday, as we await the surface low now in eastern Arkansas. As it approaches and moves north, it swings a strong cold front at least to the Blue Ridge during the late morning through aftn hrs. As winds begin to veer to west look for MVFR rain and MVFR- IFR ceilings to result mainly affecting Bluefield, Lewisburg and Blacksburg. Appears that the front will likely move through Roanoke after 00z. Medium confidence in ceilings, visibilities and winds during the taf period. Extended Discussion... Degradation in aviation conditions expected at most TAFs Saturday evening as cold front makes slow progress eastward. Period of sub-VFR rain and low ceilings to result, and gusty northwest winds expected immediately and in the several hours after the frontal passage. Model guidance varies on how quickly the front will exit the region. Lingering sub-VFR conditions may very well persist into Sunday, at least in the upsloping areas of the west, such as at KBLF, KLWB, and KBCB. MVFR snow and rain showers are also possible in the mountains Sunday night into Monday as the main brunt of colder air finally arrives. Arrival of surface high pressure should support a return to VFR weather at all terminal forecast sites with no flight restrictions Tuesday into Wednesday. Sub-vfr conditions are possible Thursday into Friday with potential wintry precipitation. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...AMS/KK NEAR TERM...AL/KK/WERT SHORT TERM...RCS LONG TERM...RCS AVIATION...AL/KK
Area Forecast Discussion
National Weather Service Tulsa OK
905 PM CST Fri Dec 22 2017 ...UPDATE... .DISCUSSION... A little bit of everything going on this evening...with exiting thunderstorms across far southeast OK and a wide variety of rain/freezing rain/sleet and snow across much of the remainder of the forecast area. 00Z OUN sounding showed an impressive warm layer from 900-700mb ensuring that much of the precip was falling as sleet this evening (with some freezing rain mixed in) over most of northeast OK. Radar suggests that we`ll see a brief lull in precipitation later this evening before another area of mostly snow associated with the upper low lifts into the region. The last several runs of the HRRR seem to have a reasonable handle on the situation...with the deformation zone setting up across northeast OK into northwest AR/southwest MO later tonight. Highest snow totals look to set up from near Tulsa and points east-northeast (also supported by recent SREF plumes)...with 1-2 inches possible although there could be isolated spots that get 3-4 inches. Lowered PoPs some across southeast OK where the dry slot is working in...and also kept a mention of freezing rain for northeast OK the remainder of the evening hours. && .PRELIMINARY POINT TEMPS/POPS... TUL 28 42 26 40 / 90 0 0 0 FSM 36 47 34 44 / 90 20 0 10 MLC 30 46 32 45 / 90 0 0 0 BVO 25 42 20 39 / 50 0 0 0 FYV 31 40 28 38 / 90 20 0 10 BYV 31 40 28 36 / 90 30 0 10 MKO 30 44 28 42 / 100 10 0 0 MIO 28 38 24 37 / 90 10 0 10 F10 30 45 29 41 / 90 0 0 0 HHW 34 48 34 49 / 80 0 0 0 && .TSA WATCHES/WARNINGS/ADVISORIES... OK...Winter Weather Advisory until 6 AM CST Saturday for OKZ055>058- 060>070. Winter Weather Advisory until 4 AM CST Saturday for OKZ054-059. AR...Winter Weather Advisory until 6 AM CST Saturday for ARZ001-002- 010-011. && $$ SHORT TERM...18